Int. J. Plant Sci. 169(7):954–962. 2008.
" 2008 by The University of Chicago. All rights reserved.
1058-5893/2008/16907-0013$15.00 DOI: 10.1086/589699
THE BIOGEOGRAPHY OF PLANTAGO OVATA FORSSK. (PLANTAGINACEAE)
Stephen C. Meyers1 and Aaron Liston
Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331, U.S.A.
Plantago ovata Forssk. (Plantaginaceae) is a species that, in North America, inhabits desert and Mediterranean
habitats of the southwest United States, northwest Mexico, and the Channel Islands of California and Mexico. In
the Eastern Hemisphere, P. ovata inhabits desert regions ranging from the Canary Islands, across northern Africa
to India. Previous authors have hypothesized that P. ovata was introduced to North America from Asia during the
Miocene or introduced anthropogenically from Europe during the eighteenth century by Spanish settlers. We
examined sequence data from the chloroplast trnL-trnF, trnS-trnG, and psbA-trnH regions, the nuclear ribosomal
internal transcribed spacer (ITS), and a putative CYCLOIDEA-like gene. Using a molecular clock based on an ITS
calibration and a clock for plant chloroplast, we date a nonanthropogenic introduction event, from the Old World
to North America, of ;200,000–650,000 yr ago. On the basis of a morphological survey of 585 specimens from
throughout the world range of P. ovata, we suggest the recognition of four subspecific taxa. Phylogenetic analysis
of chloroplast and ITS sequences supports this taxonomic treatment. Furthermore, morphological data and the
CYCLOIDEA-like gene sequences suggest the origin of North American P. ovata as a result of hybridization
between Old World P. ovata varieties.
Keywords: Plantago ovata, biogeography, hybridization, desert disjunct.
Introduction
California, Mexico, and northwestern Mexico. Palm Springs,
California, as an example, averages less than 150 mm of precipitation annually, and average midsummer temperatures are
more than 40!C. The second environment is the coastal sage
scrub of California and the Channel Islands of California and
Mexico, which have a wetter, often foggy environment. With
an average annual precipitation of 280 mm and average midsummer temperatures less than 17!C, Avalon, California, typifies this area (Western Regional Climate Center 2007).
On the basis of morphological (Rahn 1979) and molecular
(Rønsted et al. 2002) phylogenies, P. ovata belongs to Plantago
subgenus Albicans section Albicans. With the exception of P.
ovata, all taxa in this section are restricted to the Mediterranean–
southwest Asian region. The wide disjunction between P. ovata
in the Western and Eastern hemispheres poses a question as to
its origin and biogeography.
Stebbins and Day (1967) first addressed the biogeography
of P. ovata. They recognized the lack of close relatives of
P. ovata in North America and hypothesized that the species
originated in the Old World, followed by an introduction
event to the New World. They grew 12 accessions of P. ovata
from seed sources from both the Old and New World. They
found differences between Old and New World plants in cytology, pubescence of the bracts and rachis, the shape of the
bracts, and flower color. On the basis of these differences,
they divided P. ovata into two distinct species, P. ovata in the
Old World and Plantago fastigiata in the New World. At the
conclusion of their study, Stebbins and Day hypothesized
an introduction event of P. ovata from the Old World to the
New World over the Bering land bridge during the Miocene,
;20–35 million years ago.
An alternative introduction hypothesis was proposed by
Bassett and Baum (1969). Using herbarium specimens, they
Wide disjuncts between closely related plant taxa have been
and continue to be of great interest to botanists (Thorne 1972;
Wen 2001; Nie et al. 2006). For example, the North American
southwest and the Mediterranean–southwest Asian regions
have little overall similarity in their floras (Stebbins and Major
1965; Shmida 1985). However, Plantago is one of ;35 genera
that have representative species in both regions (Stebbins and
Day 1967; Thorne 1972). The disjunction between the two regions is ;13,000 km. Determining the timing and method by
which many of these disjunctions occurred has been a subject
of numerous studies (Stebbins and Major 1965; Stebbins and
Day 1967; Basset and Baum 1969; Liston and Kadereit 1995;
Coleman et al. 2003). Additionally, hybridization may play a
role in the formation of closely related, disjunct plant taxa
(Stebbins 1969). Potential examples include Hawaiian Madiinae (Barrier et al. 1999), Microseris (Vijverberg et al. 1999),
and Senecio mohavensis (Coleman et al. 2003).
Plantago ovata Forssk. (Plantaginaceae) is a winter annual
that primarily inhabits desert regions of the Northern Hemisphere between the twenty-sixth and thirty-sixth latitudes (fig.
1a). The species has two main geographic areas of distribution. In the Old World, P. ovata is found along the drier parts
of the Mediterranean Sea and southwestern Asia, extending
from the Canary Islands to western India. In the New World,
the species is found in two distinct ecological areas. The first
is the xeric environment of the North American Sonoran and
Mojave deserts of the southwestern United States, inland Baja
1 Author for correspondence; e-mail: meyersst@science.oregonstate
.edu.
Manuscript received July 2007; revised manuscript received December 2007.
954
Fig. 1 a, Locations of 585 specimens surveyed from throughout entire world range of Plantago ovata. b, Wide spike typical of Asian and
African plants (left); narrow spike typical of North American plants (right). c, Long trichomes typical of North American and African plants. d,
Short trichomes typical of Asian plants. e, Spike widths mapped as a gradient from 6.75 mm (red) to 9.95 mm (green). f, Trichome lengths map.
Green circles indicate specimens with long trichomes (>1/3 length of bracts); red circles indicate specimens with short trichomes (<1/3 length of
bracts). g, Corolla lobe length/width ratio mapped as a gradient from a low ratio (from 0.9; green) to a high ratio (to 1.7; red). h, Bract midrib
color map. Green circles indicate specimens with green bract midribs; brown circles indicate specimens with brown bract midribs. i, Brown bract
midrib typical of North American island/coastal plants. j, Green bract midrib typical of North American inland/desert plants. k, Corolla midrib
color map. Green circles indicate specimens without a prominent reddish-brown midrib. Brown circles indicate specimens with a prominent
reddish-brown midrib. l, Prominent reddish-brown midrib typical of North American island/coastal plants. m, Lack of prominent reddish-brown
midrib typical of North American inland/desert plants.
956
INTERNATIONAL JOURNAL OF PLANT SCIENCES
reexamined the same morphological characters surveyed by
Stebbins and Day (1967). In addition, they also examined pollen grain morphology. Bassett and Baum failed to find, in their
opinion, enough significant morphological differences between
Old and New World plants to justify separating plants from the
two regions into distinct taxa. On the basis of these observations, they judged P. ovata and P. fastigiata to be conspecific.
Moreover, they proposed that P. ovata was introduced anthropogenically from the Old World to the North American Southwest by Spanish settlers during the eighteenth and nineteenth
centuries. Dried seeds of Plantago species have and continue to
be used as an aid to relieve constipation and treat severe diarrhea (Hoffman 1998; Foster and Duke 1999). The anthropogenic introduction hypothesis, proposed by Bassett and Baum,
is implicitly accepted by modern floras (Wallace 1985; Beauchamp 1986; Dempster 1993; Junak et al. 1995).
The last major study of P. ovata before our research was conducted by Rahn (1979). Unlike the previous studies, which
were qualitative and did not include an explicit analysis of morphology, Rahn surveyed morphological characters of 391 herbarium specimens from throughout the range of P. ovata. Rahn
found a statistical difference in corolla length and width as well
as spike width between Old and New World plants. In addition, a statistical difference was found in corolla length/width
ratios between African plants and those of Asia and the New
World. Rahn, however, did not consider these differences sufficient to separate the regional populations of P. ovata into separate
species or subspecific taxa. He did suggest that the morphological differences between Old and New World P. ovata
were not pronounced enough to fit the hypothesis of Stebbins
and Day (1967) unless evolution within P. ovata had been very
slow. Likewise, Rahn concluded that the differences between
Old and New World P. ovata were too distinct to support the
theory of a recent anthropogenic introduction event, unless evolution within the species was extremely fast.
The goal of our study was to resolve the conflicting opinions of previous studies concerning the taxonomy, evolution,
and biogeography within P. ovata. To do so, we analyzed both
morphological and molecular sequence data obtained from
specimens throughout the world range of P. ovata.
The DNA sequences included the nuclear ribosomal internal transcribed spacer region (nrITS) and three noncoding
chloroplast regions. The rate and pattern of nrITS sequence
mutation can be appropriate for resolving relationships within
plant species (Hillis and Dixon 1991; Hamby and Zimmer
1992; Doi et al. 2002). To supplement the nrITS data set, we
sequenced the noncoding chloroplast psbA-trnH, trnS-trnG,
and trnT-trnL spacer regions. In addition to nuclear and chloroplast sequences, we obtained sequences of the coxI mitochondrial gene. We chose to sequence the coxI gene as a result
of findings by Palmer et al. (2000) of highly accelerated substitution rates in the mitochondrial genome of several Plantago
species.
To analyze the potential for hybridization between subspecific taxa, we amplified, cloned, and sequenced a putative
CYCLOIDEA (CYC)-like gene. We focused on this particular
gene because it is a low copy number nuclear gene (Vieira et al.
1999). Similar genes have proven useful in phylogenetic studies
involving hybridization (Olsen and Schaal 1999; Sang and
Zhang 1999; Small et al. 2004; Kim and Donoghue 2005).
Material and Methods
A total of 585 specimens obtained from herbaria or collected
in the field from throughout the world range of Plantago ovata
was analyzed (fig. 1a). We recorded all morphological characters used by previous authors, with the exception of pollen and
chromosome morphology (spike width; corolla width and
length; trichome length; bract and leaf pubescence presence;
bract midrib, corolla, and leaf color). Additionally, spike length,
plant size, seed coat color, and callous-teeth presence were surveyed on each specimen.
The principal components analysis (PCA) and statistical
analysis of the morphological data were performed using Statgraphics Plus software (ver. 5.1; Manugistics, Rockville, MD).
For the PCA, specimens were delineated by region (Africa, Asia,
island/coastal North America, and inland/desert North America).
To estimate a phylogeny, we used 2153 base pairs (bp) of
DNA sequenced from 14 specimens from throughout the
world range of P. ovata. DNA was obtained from fresh plant
material and dried herbarium specimens (table 1). We used
;50 mg of plant material to extract DNA using a DNeasy
Plant Mini Kit (Qiagen, Valencia, CA).
Primers for the mitochondrial coxI gene were designed from
the alignment of previously published coxI sequences of Plantago specimens and yielded ;1600 bp of product. Sequences for
the primers are 59-ATCTYCAACATGCGTGG-39 and 59-CCAAKAAAGGTGATCC-39. Amplifications of the coxI gene were
performed following the protocol described by Palmer et al.
(2000). All other primers were obtained from and amplified following the protocols of Taberlet et al. (1991), Liston et al. (1996),
Vieira et al. (1999), and Shaw et al. (2005).
CYC-like sequences were obtained from four specimens representative of the four clades resolved in the molecular phylogeny. Twelve clones from each North American specimen and
10 clones from each Old World specimen were sequenced (44
total). A CYC-like sequence of Digitalis pupurea was obtained
from GenBank (AF146865) as an outgroup.
Clones from the initially obtained CYC PCR reactions were
constructed and amplified using a Qiagen PCR cloning plus
kit (Qiagen) according to the manufacturer’s instructions. Following PCR, all products were purified using QIAquick PCR
purification kits (Qiagen).
Sequencing was performed by Macrogen (Kumchun-Ku,
Seoul) and Northwoods DNA (Solway, MN). Sequences were
aligned by eye and analyzed using BioEdit for Windows 95/98
(Hall 1999). To test whether individual chloroplast and nrITS
trees should be combined and whether topologies among
the trees were significantly different, Templeton and KishinoHasegawa tests (Templeton 1983; Kishino and Hasegawa 1989)
using PAUP* were employed.
Phylogenetic analyses were conducted using PAUP* (ver. 4b10;
Swofford 2002) and MrBayes (ver. 3.0b4; Huelsenbeck and
Ronquist 2001). For individual and combined sequences, the
most parsimonious trees were found using branch and bound
maximum parsimony searches within PAUP*, employing the
furthest addition sequence setting and MulTrees on. Gaps were
scored as missing data. Branch support was assessed using 1000
bootstrap replicates. Modeltest 3.06 (Posada and Crandell 1998)
was used to select the model rate that best fit each data set. A
general-time-reversible (GTR) model incorporating a gamma
MEYERS & LISTON—BIOGEOGRAPHY OF PLANTAGO OVATA
957
Table 1
Specimens Analyzed for DNA Sequence Data and Regions Sequenced
Location
Africa:
Egypt; between Cairo and Alexandria
Morocco; 50 km NE of Tan-Tan
Tunisia; Medenine
Asia:
Afghanistan; Kunar Prov., Darrah-i-Khor
Iraq; 16 km SE of Badra
Israel; Negev Highland, En Avdat
Inland/desert North America:
USA; California; Riverside Co.; Thousand Palms
USA; California; San Bernardino Co.; Zzyzx
USA; California; Imperial Co.; Desert Shores
Mexico; Baja California Norte; Catavina
Island/coastal North America:
USA; California; Ventura Co.; San Nicolas Island
USA; California; Ventura Co.; West Anacapa Island
USA; California; Los Angeles Co.; Santa Catalina Island
Mexico; Baja California Norte; San Quentin
Collector
Regions sequenced
Podlech 49375 (MSB)
Podlech 45139 (RSA)
Ullman s.n. (MSB)
ch, nu
mi, ch, nu, CYC
ch, nu
Podlech 20228 (MSB)
Rechinger 9218 (BSM)
Danin s.n. (OSC)
ch, nu
ch, nu
mi, ch, nu, CYC
Meyers
Meyers
Meyers
Meyers
179
182
219
205
mi, ch, nu, CYC
ch, nu
ch, nu
ch, nu
Thorne
Blakley
Meyers
Meyers
52410 (RSA)
5804 (SBG)
225 (OSC)
201 (OSC)
(OSC)
(OSC)
(OSC)
(OSC)
ch,
ch,
ch,
ch,
nu
nu
nu, CYC
nu
Note. Abbreviations: mi ¼ mitochondrial coxI region; ch ¼ chloroplast trnT-trnL, trnS-trnG, and psbAtrnH spacer regions; nu ¼ nuclear ribosomal ITS region; CYC ¼ CYCLOIDEA-like gene. For herbarium codes,
see Holmgren et al. (1990). GenBank accession numbers EU036229–EU036294.
distribution was selected for each data set and used during all
Bayesian searches. Bayesian searches were conducted with
four simultaneous Markov chains over 2 million generations,
sampling every 100 generations. All trees generated within the
burn-in period (20,000) were discarded, and posterior probability confidence values were based only on trees found in the
stationary phase.
To evaluate whether sequences diverged at clocklike rates,
maximum likelihood trees were estimated using the GTR þ g
model as implemented in PAUP*. Again using PAUP*, pairwise
distances between taxa and mean nucleotide differences, adjusted for missing data, were obtained. Data from combined
chloroplast sequences (2076 bp) were used in a molecular clock
calculation for plant chloroplast at a rate of 2:5 3 10"9 substitutions per site per year (Wolf et al. 1987; Muse 2000; Herbert
et al. 2002; GuhaMajumdar and Sears 2005). A molecular
clock calculation for the nrITS sequences (605 bp) was completed using a rate of 4:27 3 10"9 substitutions per site per year.
The later calculation was based on a geological calibration
within the Plantago genus by Rønsted et al. (2002) of a dispersal
event to a dateable oceanic island. Divergence dates were calculated using the following formula: pairwise distance/substitution
rate 3 2 ¼ years since divergence.
Results
Individual parsimony trees constructed for each of the three
chloroplast and nrITS regions sequenced shared a similar topology. The Templeton and Kishino-Hasegawa tests found no conflict between the separate chloroplast and nrITS data sets
(P ¼ 0:96 and 0.93, respectively). Likewise, the combined maximum parsimony consensus (not shown) and Bayesian majority rule consensus trees shared identical topology (fig. 2). This
analysis resolves the Old World group as paraphyletic, whereas
specimens from the New World are a clade. Additionally, the
Old and New World samples are each subdivided. The Old
World samples are separated as subgroups from Asia and Africa.
Likewise, within the New World group, subgroups from the inland/desert and the island/coastal regions are apparent (fig. 2).
P values of the mean nucleotide differences between Old and
New World chloroplast and nrITS sequences were calculated
to be 0.0002 and 0.0014, respectively. Using the molecular
clocks for both chloroplast and nrITS DNA, we date an introduction event of Plantago ovata from the Old World to the
New World ;200,000 (chloroplast) to 650,000 yr ago (nrITS).
Of the 13 morphological characters surveyed, five delimiting characters were found (fig. 1; table 2). These characters reliably distinguish Old World plants from New World plants.
The characters also distinguish regional plant populations
(Africa, Asia, island/coastal North America, and inland/desert
North America). The same regional plant populations formed
clusters within the graphical results of the PCA (fig. 3).
North American plants share unique characters with both
Asian and African plants that the Asian and African plants
do not share with each other (fig. 1b–1g; table 2). Specifically,
North American plants share long trichomes with African
plants and a large corolla length/width ratio with Asian plants.
This supports the fact that North American plant morphology
may be the result of a hybridization event between Asian and
African plants. Within the PCA graph, specimens from North
America are found clustered between the groups of specimens
from Asia and Africa (fig. 3). This result also reflects the potential for an African-Asian hybridization event.
A total of four unique cloned CYC sequences were found
within the North American specimens. Bayesian and maximum parsimony (not shown) majority rule consensus trees
constructed from those sequences display two resolved clades
(fig. 4). Two of the North American sequences were identical
INTERNATIONAL JOURNAL OF PLANT SCIENCES
958
Fig. 2 Results of the Bayesian inference of phylogeny of combined nuclear and plastid sequences. Numbers above branches indicate posterior
probabilities and bootstrap values, respectively. For maximum parsimony analysis, consistency index ¼ 0.84, retention index ¼ 0.92.
to the single Asian and African sequences found. Another two
North American sequences are divergent but are contained
within the two clades, respectively. This topology is consistent
with the hypothesis that the North American taxa of P. ovata
are of hybrid origin between the two Old World taxa.
Discussion
Although Palmer et al. (2000) found highly accelerated substitution rates in the mitochondrial genome of several Plantago
species, in the specimens we compared, no sequence divergence
was found. As a result, those sequences were not utilized.
Hybridization
Hybridization has been recognized as a widespread and important mode of evolution in plants, especially as a source of
new plant taxa through diploid hybridization (Rieseberg
1995, 1997; Wolfe et al. 1998; Gross et al. 2003). A potential
subspecific hybridization event within Plantago ovata has not
been addressed in previous studies of the species (Stebbins and
Day 1967; Bassett and Baum 1969; Rahn 1979). Although the
morphological data collected by Rahn (1979) are consistent
with a potential hybridization event between Asian and African P. ovata populations and subsequent dispersal to North
America, he did not address that issue.
Typically, to analyze a hybridization event in a molecular
study, nuclear DNA sequences are analyzed. While we did
have nrITS sequence data, in contrast to many other plants
(Sang et al. 1995; Whittall et al. 2000), nrDNA additivity was
not observed in the P. ovata specimens sequenced.
A previous study has located three to four copies of CYClike genes in the plant order Dipsacales (Hileman and Baum
2003). The Dipsacales and Plantaginaceae are both Asterids;
therefore, numerous copies may exist in P. ovata as well. Although locus number in Plantago is unknown, our results are
consistent with the presence of two CYC-like loci, as required
by the presence of three putative alleles (sequences) in the
Table 2
Five Informative Characters That Differentiate Regional Populations of Plantago ovata
Bract midrib
color
Corolla midrib
color/length
Spike width (mm)
Corolla length/width ratio
Trichome length
Average
SD
Range
Average
SD
Range
Asia
Africa
Inland/desert
North America
Green to brown
Green to brown
Variable
Variable
<1/3 length of bracts
>1/3 length of bracts
9.95
9.72
1.40
1.10
8–14
6–13
1.42
1.12
.1
.10
1.31–1.92
.90–1.30
Green
None to light, <1/2
length of corolla
>1/3 length of bracts
7.00
1.10
4–10
1.43
.13
1.20–1.81
Coastal/island
North America
Brown
Dark, >1/2 length
of corolla
>1/3 length of bracts
6.14
1.26
2–9
1.56
.15
1.21–2.16
MEYERS & LISTON—BIOGEOGRAPHY OF PLANTAGO OVATA
Fig. 3 Principal components analysis of morphological characters
surveyed. North American specimens (squares and circles) are intermediate to African and Asian specimens. The first axis accounts for 48.6%
of the variation. The second axis accounts for 39.2% of the variation.
959
thors have made successful crosses between Old and New
World plants, no crosses between African and Asian plants
have been attempted (Stebbins and Day 1967). This may prove
to be an interesting area for future study.
Long-distance nonanthropogenic dispersal following hybridization is well documented in plant taxa (Wallace and Jansen 1990; Barrier et al. 1999; Vijverberg et al. 1999). Senecio
mohavensis ssp. mohavensis geographically represents a hybridization example similar to P. ovata. Senecio mohavensis
ssp. mohavensis is a North American desert species that has
been indicated to be a hybrid between the African Senecio
taxa Senecio flavus and Senecio glaucus (Liston and Kadereit
1995; Comes and Abbott 2001). Following a tetraploid hybridization event, S. mohavensis ssp. mohavensis was apparently introduced to North America during the Pleistocene era
(Liston et al. 1989; Coleman et al. 2001; Coleman et al. 2003).
Plantago ovata provides another example of an apparent hybrid that has become successfully established after a nonanthropogenic introduction event.
Introduction into North America
North American island/coastal accession. Assuming that two
loci are present in the Old World accessions, the single CYClike sequence each possesses may be the result of interlocus
concerted evolution. Alternatively, there could be a single
locus in Old World P. ovata and a gene duplication in the derived North American clade. In either scenario, the combination of CYC-like sequences from the two resolved clades in
both North American accessions is indicative of hybridization
between Asian and African populations (fig. 4).
Molecular data from a specimen from the Sinai Peninsula,
where hybrids of the African and Asian varieties may exist,
would be very desirable. Unfortunately, several attempts to
extract and amplify DNA from Sinai Peninsula herbarium
specimens failed, likely because all specimens were more than
30 yr old. Likewise, because only eight specimens were obtained from the Sinai Peninsula, conclusions based solely on
morphological data were not drawn. Although previous au-
We date an introduction event of P. ovata from the Old
World to North America 200,000–650,000 yr ago, during the
Pleistocene. This is ;19 million years after the date proposed
by Stebbins and Day (1967). The estimated age of crown
group diversification within the Plantago genus is 5.47 million
years ago (Rønsted et al. 2002), a date nearly 15 million years
after the introduction date Stebbins and Day propose.
Our introduction date is also very distant from the eighteenthto nineteenth-century date hypothesized by Basset and Baum
(1969). Our molecular dating precludes any anthropogenic introduction event. In addition, other evidence suggests that
Spanish settlers would not likely have been the vehicle for the
introduction of P. ovata into North America. While P. ovata
has and continues to be used as a medicinal herbal remedy, its
use during the eighteenth and nineteenth centuries was largely
restricted to Ayurvedic practitioners in Asia, in particular, India (Jain and DeFilipps 1991).
Fig. 4 Bayesian inference of phylogeny of CYCLOIDEA-like sequences. Posterior probabilities above branches.
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INTERNATIONAL JOURNAL OF PLANT SCIENCES
Although P. ovata inhabits a small portion of the southern
Iberian Peninsula, it is far more likely that Spanish settlers
would have used a more common Plantago species as an herbal
medicine. For example, Plantago major and Plantago lanceolata,
common in Spain and established in North America after European introduction during the eighteenth and nineteenth centuries, was and is used for the same medicinal effects as P. ovata
(Schauenberg and Paris 1977).
Our introduction date of P. ovata from the Old World into
North America 200,000–650,000 yr ago is similar to the introduction date of S. mohavensis ssp. mohavensis from the
Old World into North America ;150,000 yr ago. These dates,
however, differ greatly from other estimates of Mediterranean–
North American introductions. Datisca, for example, was calculated to have reached western North America from Eurasia
10–50.5 million years ago (Liston et al. 1992; Liston 1997).
Other examples are the introduction of Styrax to North America,
estimated at 5–13.8 million years ago (Fritsch 1996), and Aphanisma, which was calculated to have arrived in North America
14.6–20.3 million years ago (Hohmann et al. 2006). Assuming that the calculated introduction dates are correct or even
roughly accurate, a bimodal (Miocene-Pleistocene) series of
Mediterranean–western North American introductions may
have occurred. Whether the route or mechanism for each of
these introductions has a similar pattern is not currently
known. While other disjunctions, such as the eastern Asia–
eastern North American disjunction, have been extensively
studied (Wen 2001), comparatively fewer studies have researched the Mediterranean–western North American disjunction (Hohmann et al. 2006). As the biogeography of more
Mediterranean–western North American disjunct taxa is investigated, patterns are likely to emerge.
The mechanism of the introduction of P. ovata into North
America can only be speculated at this point. The seeds of P.
ovata are not suitable for wind dispersal, but similar to the
seeds of S. mohavensis ssp. mohavensis, which become mucilaginous when wet, dispersal via epizoochory is a possibility.
It should be noted, however, that mucilage is thought to be
connected with germination rather than dispersal (Sorensen
1986). It is also worthwhile to note that during the Pleistocene, extensive wetland habits were common in both Asia/
North Africa (Cox and Moore 1993) and southwest North
America (Schaffer 1993). While bird migration between Asia/
North Africa and southwest North America is unknown today, ecological conditions during the Pleistocene epoch may
have been more favorable for such a migration to occur.
Taxonomic Implications
Our morphological findings are similar to those of Rahn
(1979), who did not suggest the recognition of subspecific taxa
within P. ovata. However, on the basis of our survey of 585
specimens versus Rahn’s 391 specimens, we propose the recognition of four subspecific taxa within P. ovata.
Within North America, we propose recognition of two varieties of P. ovata. The inland/desert variety, P. ovata var. fastigiata, is found in xeric desert habitats. Plantago ovata var.
fasigiata is morphologically different from the Old World varieties by nature of its narrow spike width (fig. 1b, 1e). This
variety is distinguished from the other North American vari-
ety, P. ovata var. insularis, by the green bract midrib of its mature flowers and corolla lobes with little or no dark brown/red
coloration (fig. 1h–1m).
The second North American variety, P. ovata var. insularis, is
found in coastal sage scrub habitats and on hilltops and basins
of the Channel Islands of California and Mexico (fig. 1). Like
P. ovata var. fastigiata, P. ovata var. insularis differs from the
Old World varieties of P. ovata by its narrow spike width (fig.
1b, 1e). Plantago ovata var. insularis is easily distinguished
from P. ovata var. fastigiata by brown bract midribs found on
mature flowers and corolla lobes with wide dark brown/reddish
coloration found on the midrib (fig. 1h–1m).
The recognition of subspecific taxa based on combined morphological and environmental distinctions is quite common.
For example, Limnanthes floccosa ssp. grandiflora, found on
the wetter, inner fringes of vernal pools, has large corollas and
sparse pubescence, while L. floccosa ssp. floccosa, found on the
drier, outer fringes of the same vernal pools, has small corollas
and denser pubescence (Arroyo 1973). Our conservative recognition of the two North American P. ovata taxa as varieties is
well within the bounds of conventional naming tradition.
Within the Old World, we propose recognition of two varieties. Plantago ovata var. decumbens is found in Asia, from the
Sinai Peninsula in the east to west India. Plantago ovata var.
decumbens is distinguished from the other Old World variety,
P. ovata var. ovata, by a typical corolla length to width ratio
greater than 1.3 (fig. 1g) and trichomes beneath the spike less
than 1/3 the length of the bracts (fig. 1c, 1d, 1f ).
The second Old World variety, P. ovata var. ovata, is found
in the geographic area from the Canary Islands east to the Sinai Peninsula. This variety is distinguished from P. ovata var.
decumbens by its corolla length to width ratio typically less
than 1.3 (fig. 1g) and trichomes longer than 1/3 the length of
the bracts (fig. 1c, 1d, 1f ).
We have chosen to recognize these four taxa as varieties
and not subspecies because, while they are morphologically
distinct, the taxa within the Old and New Worlds are not separated by a limiting geographic or environmental barrier and
likely intergrade. The two varieties within the Old and New
Worlds could potentially be consolidated into two subspecies
consisting of two Old and New World subspecies. This consolidation, however, would result in the naming of taxa with
quadrinomials. These names, while accurate, are cumbersome
and not likely to be broadly accepted. We do not believe that
recognition of these taxa at the species rank is warranted either. Within Plantaginaceae, the splitting of taxa is traditionally conservative (Rahn 1979). While the taxa we recognize
are distinct, the differences are not extensive enough to warrant naming at the species rank.
Key to Plantago ovata
1. Corolla lobe length/width ratio 0.9–1.3; Africa . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . P. ovata var. ovata
1. Corolla lobe length/width ratio (1.2) 1.3–1.7
2. Trichome length <1/3 length of bracts; Asia . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . P. ovata var. decumbens
2. Trichome length >1/3 length of bracts
3. Usually a prominent reddish-brown midrib on corolla
lobes; bract midrib of mature flowers brown; coast sage scrub
MEYERS & LISTON—BIOGEOGRAPHY OF PLANTAGO OVATA
of North America and Channel Islands of California and Mexico . . . . . . . . . . . . . . . . . . . . . . . . . . . . P. ovata var. insularis
3. Corolla lobes usually without a reddish-brown midrib;
bract midrib of mature flowers green; inland deserts of North
America . . . . . . . . . . . . . . . . . . . . . . . . P. ovata var. fastigiata
Plantago ovata Forssk. var. ovata—Fl. Aegypt. Arab.:31,
1775—Type: Forsskal 253#,2 designated by Rahn, 1979 (C
lectotype#, 249 and 250 isolectotypes#). For synonymy, see
Rahn (1979).
Plantago ovata Forssk. var. decumbens (Forssk.) Zohary—
Palestine Journ. Bot. ser. 1:227, 1938–40. Plantago decumbens
Forssk.,—Fl. Aegypt. Arab.:30, 1775—Types: Forssk. 254 and
259, we designate 259 as lectotype (C lectotype#, isolectotype#). For synonymy, see Zohary (1938).
Plantago ovata Forssk. var. insularis (Eastwood) S. Meyers
& A. Liston, comb. nov.—Plantago insularis Eastwood, Proc.
Calif Acad. Sci. 3,1:112, 1898—Type: Trask s.n. (CAS holotype!, K isotype). No synonyms exist.
Plantago ovata Forssk. var. fastigiata (Morris) S. Meyers &
A. Liston, comb nov.—Plantago fastigiata Morris, Bull. Torrey Bot. Club 27:116, 1900—Plantago insularis Eastwood
var. fastigiata (Morris) Jepson, Man. Fl. Pl. Calif.; 956,
1925—Type: Toumey 355a, designated by T. Ayers, 1998. We
confirm this lectotypification (US lectotype#, isolectotype#).
961
Synonymy. P. minima A.M. Cunningham, Proc. Indiana
Acad. Sci. 1896: 202.—P. scariosa Morris, Bull. Torrey Bot.
Club 27: 117, 1900.—P. insularis Eastwood var. scariosa
(Morris) Jepson, Man. Fl. Pl. Calif.: 956, 1925.—Types: Bailey
s.n. (US paratype#), Coville & Funston 678 (US paratype#),
Palmer s.n. (US lectotype#). We designate Palmer s.n. as lectotype.
P. brunnea Morris, Bull. Torrey Bot. Club 27: 115, 1900.—
P. fastigiata Morris var. brunnea (Morris) Pilger, Das Planzenreich IV 269: 374, 1937.—Type: Palmer 654 (US holotype#,
K,F, isotypes).
P. gooddingii Nelson & Kennedy, Muhlenbergia 3:142–
143, 1908.—Type: Goodding 808a.
Acknowledgments
We would like to thank the following herbaria for the loan
of specimens required for this study: ASU, CAS, FI, M, RSA,
SBBG, W, and UC. We are also indebted to J. Andrew Alexander
(OSC), Avinoam Danin (HUJ), and Richard Halse (OSC) for
assistance with collecting plant material. We also thank two
anonymous reviewers and the editor for helpful comments on
the manuscript.
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